Shoes are unfortunately prone to mould, especially in humid climates.
Ventilation is one of the best ways to reduce the proliferation of mould- how much ventilation do you need though?
Just as opening one window in your home doesn't bring the breeze in as much as opening two windows does, having just one vent in a wardrobe or cabinet doesn't encourage movement through the interior.
So when mould is an issue, it's best to have vents in as many places as possible, upper, lower, left and right.
I find adding laser mesh, which is available in many designs, is an attractive way to achieve this functionality.